a. Field of the Invention
The present invention relates generally to surveying instruments for taking measurements in utility manholes, and, more particularly, to an apparatus for taking measurements of inverts and other features within a manhole using a rotating rod that is mounted centrally within the opening of the manhole for obtaining measurements of the height, horizontal distance and angular position of the features.
b. Related Art
Certain utility systems, such as sewer systems, employ a multiplicity of conduits that pass beneath streets and built-up areas and that meet and are accessed at manholes at suitable locations. In the case of sewer systems, the pipes, where they enter and leave the manholes, are referred to as “inverts”.
For a variety of reasons, it is essential that the municipality or another utility owner/operator have accurate data concerning the location and orientation of the various inverts and/or other features in each manhole within its system. For example, it is critical to know the height and angular orientation of each invert in a system when planning re-lining of sewers or other renovation work. In many or most cases however, such data is not readily available. For example, in many older municipalities the inverts have been installed successively over a period of decades (or even centuries), often in an almost haphazard fashion and with little or no records being kept concerning their location or orientation. Even in comparatively modern systems, record-keeping and measurement data are often scanty or non-existent.
To address these issues, many municipalities and other utility owners have undertaken comprehensive mapping of their sewers and other systems, including measuring the height and angular orientation of all of the inverts that are accessible at the manholes. Since even a modest-sized municipality can have systems with literally thousands of pipes, inverts and so on, the scale of the mapping projects is massive, reaching extreme proportions in the case of major metropolitan areas. Moreover, the measurements must be precise, or else the collected data is useless.
The cost and difficulty of the mapping projects has been significantly compounded by the limitations of existing measuring equipment. On the whole, this has consisted of comparatively primitive, manually-operated surveying tools. FIGS. 1-2 show a typical arrangement, in which the measuring tool 10 is composed of a graduated rod 12 having a laterally-extending foot 14 mounted to its lower end. The rod is held by an operator 16 and the foot is inserted through the access opening 18 into the interior of the manhole 20, as is shown in FIG. 1. The operator guides the foot, visually and by feel, into the invert openings 22, 24, as shown in FIG. 2. The operator then reads the height from the rod, where this meets the lip of the opening 18, and estimates the angular orientation of the invert.
It will be readily understood that taking measurements in the foregoing manner is not only labor-intensive but is also fraught with opportunity for inaccuracies. It is difficult or impossible for the operator to simultaneously hold/manipulate the rod and record the measurements, so that frequently a two-man team is required and even then the process is slow and laborious. Also, the accuracy of the measurements is highly suspect: for example, the accuracy of the height measurement is dependent on the rod being held precisely upright and at the exact reference point on the manhole lid/seat (which frequently is not flat), which is especially difficult in the cases of large-diameter manholes and angled inverts. Furthermore, although certain expediencies have been adopted by some operators, judging the angular orientation of the inverts is a somewhat subjective art at best, to the point that measurements taken at a single manhole may vary significantly from one operator to the next. Still further, pipe out-of-roundness and manhole eccentricity cannot be effectively measured using this method. Even after the measurements have been obtained, the steps of sketching the manhole and transferring the typically handwritten measurements to an electronic database, which is essential for their subsequent use, is itself a laborious process and offers yet additional opportunities for mistakes and errors.
In combination, these factors present a serious problem for the entity that is conducting the mapping operation. The multiple steps and labor-intensive character of the process translate to a very high cost. Moreover, even when the mapping has been completed the accuracy of the data remains suspect, to the point where the utility owner often cannot rely on it and a second set of measurements must be taken before commencing a project, since the financial consequences of erroneous measurements can be catastrophic in a major project, such as the installation or renovation of a sewer line.
Accordingly, there exists a need for an apparatus for measuring both the elevation and angular orientation of inverts in a manhole that obtains the measurements in a rapid and efficient manner. Furthermore, there exists a need for such an apparatus that renders it easy for only a single operator to both take and record the measurements. Still further, there exists a need for such an apparatus that is capable of obtaining the height and angular orientation measurements of inverts with a high degree of accuracy. Still further, there exists a need for such an apparatus that is capable of collecting the measurement data in electronic form, so as to eliminate the need for the intermediate step of translating written or other manually-entered information to an electronic database.